US20060188264A1 - Polarization diversity for optical fiber applications - Google Patents
Polarization diversity for optical fiber applications Download PDFInfo
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- US20060188264A1 US20060188264A1 US11/062,649 US6264905A US2006188264A1 US 20060188264 A1 US20060188264 A1 US 20060188264A1 US 6264905 A US6264905 A US 6264905A US 2006188264 A1 US2006188264 A1 US 2006188264A1
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- 230000010287 polarization Effects 0.000 title claims abstract description 87
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- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
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- the invention relates generally to optical signal transmission and is particularly, but not exclusively, suited for systems where phase information is transmitted over an optical cable to a remotely located optical receiver where the optical cable is subject to vibration due to the external environment.
- Optical cable is utilized in a variety of applications to carry information that is modulated onto a beam of light. In some applications significant portions of the optical cable are in an environment where the optical cable is not normally subjected to substantial physical vibration. In other applications optical cable is utilized to carry information between two locations where the optical cable is subject to substantial movement, flexing or vibration.
- FIG. 1 illustrates an example of an application where the optical cable 10 is subject to substantial movement.
- phase information is transmitted from a towed array 12 of acoustic sensors towed behind a watercraft 14 to an optical receiver 16 in the watercraft.
- An optical sensor 18 may use a Mach-Zehnder interferometer as described in U.S. Pat. No. 5,448,058 and incorporated herein by reference.
- One or more light beams carrying the sensed information are transmitted to the optical receiver by one or more optic fibers in optical cable 10 .
- a light source e.g. a laser, is associated with the receiver 16 and transmits a light beam on one fiber of the cable 10 as an input to the sensor which is typically a passive device such as an interferometer.
- Another cable 20 e.g. a steel cable, absorbs the forces required to pull the sensor array through the water.
- the optical cable experiences substantial physical movement, i.e. low-frequency vibration typically below 50 hertz known as tow cable strum.
- Movement of an optical cable carrying information encoded on a light beam can give rise to a change in the state of polarization of the transmitted light. Unwanted changes in the state of polarization of the transmitted light such as due to tow cable strum are manifest as polarization noise at the optical receiver.
- Polarization diversity detection has been utilized in an optical receiver to overcome polarization fading.
- the desired signal can disappear at the optical receiver due to polarization fading such as when the two light beams in a Mach-Zehnder interferometer are orthogonal.
- a polarization diversity receiver is described in U.S. Pat. No. 5,852,507, which is incorporated herein by reference.
- Polarization optics or masks have been employed at the receiver adjacent to the detector elements to achieve polarization diversity reception.
- the invention in one implementation encompasses an apparatus.
- the apparatus includes at least one polarization beamsplitter that receives as an input a single light beam carrying sensor information and produces two light beams with polarization diversity. These two beams each carry sensor information contained in the single originating light beam.
- This apparatus is located at or near the point of origination of information that is to be conveyed to a remotely located optical receiver. Separate optic fibers carry each of the two beams to the remote location where the information is recovered by an optical receiver from the two separate light beams.
- the apparatus includes means for producing three separate light beams from a single light beam where each of the three beams is polarization diverse from the other beams.
- Three separate optic fibers carry respectively each of the three beams from the point of origination to the remote location where the information is recovered by an optical receiver from the three separate light beams.
- the method includes generating, at or adjacent the point of origination of information to be conveyed to a remotely located optical receiver, at least two light beams that are polarization diverse to each other that each carries a representation of the same information. These two light beams may be converted into two single mode type light beams. Separate optic fibers transmit the single mode light beams to the remote location where an optical receiver selects one of the light beams for decoding the signal information.
- FIG. 1 shows a known system in which an optic cable is subject to a vibration inducing environment.
- FIG. 2 is a representation of one implementation of an apparatus in accordance with the present invention in which three light beams with polarization diversity are carried by respective optic fibers through a portion of the environment that subjects the fibers to vibration.
- FIG. 3 is a representation of another implementation of an apparatus in accordance with the present invention in which two light beams with polarization diversity are carried by respective optic fibers through a portion of the environment that subjects the fibers to vibration.
- FIG. 4 is an exemplary method in accordance with the present invention.
- An aspect of the present invention resides in the recognition of the mechanism by which polarization noise occurs and in appreciating an energy transfer characteristic of a light beam carried by an optical fiber as a function of polarization changes.
- polarization diversity detection has been employed within known optic receivers, polarization noise caused by vibration of the optic fiber has provided an adverse impact in being able to accurately decode the transmitted signal.
- an inventive contribution was made when the total transmitted power of the light beam was considered from a different perspective. In traveling from the sensor output to the detector at the optical receiver, the time-dependent characteristic of the total transmitted power of the light beam should remain the same except for the overall attenuation loss. This principle applies even in the presence of undesired polarization changes due to cable vibration.
- a single light detector e.g. a photodiode
- the optical receiver which collects all of the light from a single cable should reflect the time-dependent power characteristic of the light beam with or without undesired polarization changes. Therefore, generating polarization diverse signals at or adjacent the signal source and transmitting the polarization diverse light beams on separate optic fibers, even if these fibers are subjected to vibrations causing undesired polarization changes, can be decoded by separate detectors at the optical receiver with minimized interference due to polarization noise.
- FIG. 2 illustrates an embodiment of the present invention in which a sensor system 30 transmits information by light beams carried by corresponding optical fibers to optical receiver 32 .
- This embodiment is especially, but not exclusively, suited for the transmission of information returned by acoustic sensors, e.g. interferometers, on a towed sensor array where the system 30 is on the towed sensor array and optical receiver 32 is on a watercraft that tows the array.
- the optical fibers 34 , 36 and 38 carry polarization diverse light beams transmitted from system 30 to corresponding detectors in the optical receiver 32 . These optical fibers experience substantial physical vibration, e.g.
- a light source 33 a laser, transmits a light beam carried by fiber 35 that serves as the input to sensors 42 .
- the fibers passing through region 40 may be part of one cable.
- the sensor 42 which may comprise an acoustic sensor, e.g. a Mach-Zehnder interferometer, provides an output signal as a light beam carried by a single mode fiber 44 .
- a splice 46 converts the light beam from a single mode fiber type (SMF) to a polarization maintained fiber type (PMF).
- the output light beam from splice 46 is carried by PMF 48 to a polarization maintaining beam splitter 50 , which may comprise a fiber optic implementation available from Canadian Instrumentation and Research, that splits the incoming beam into two beams.
- One output beam from splitter 50 is carried by PMF 52 to splice 54 that converts the light beam from PMF type to SMF type.
- the other output beam from splitter 50 is passed by PMF 56 to a 45° PMF to PMF splice 58 , which provides a 45° rotation of the polarization eignmstates.
- This beam is carried by PMF 60 to polarization maintaining beam splitter 62 , which may comprise a fiber optic implementation available from Canadian Instrumentation and Research that splits the incoming beam into two PMF beams.
- One output beam from splitter 62 is carried by PMF 64 to the PMF to SMF splice 66 .
- the other output beam from splitter 62 is carried by PMF 68 to PMF to SMF splice 70 .
- Splices 54 , 66 and 70 provide output light beams of a single mode type suited for being economically carried by separate SMFs 34 , 36 and 38 , respectively. Although a conversion is shown from PMF to SMF at these three splices, PMF fiber could be used to carry the light beams to the optical receiver. These three SMFs each carry a representation of the same instance (same time frame) of an output signal from sensor 42 and traverse region 40 which subjects the fibers to vibration. The light beams carried by these three fibers are terminated respectively at optical receiver 32 containing three separate photodiode detectors coupled respectively to each SMF.
- the PM fibers 56 and 60 along with a 45° PMF to PMF splice 58 are needed between splitter 50 and 62 . It is not necessary to use PMF for fibers 52 , 64 and 68 assuming that PMF fibers are not needed in order for the associated splitters 50 and 62 to work as described.
- FIG. 3 represents a further embodiment in which sensor system 130 transmits information by light beams carried by corresponding optical fibers 136 and 138 to optical receiver 132 . Since this embodiment has substantial similarities to the embodiment explained with regard to FIG. 2 , only differences will be addressed. It will be understood that elements in FIG. 3 that correspond with like elements in FIG. 2 are numbered by adding “100” to the reference numeral of the corresponding element in FIG. 2 . Basically, the 45° PMF to PMF splice 58 of the embodiment of FIG. 2 is omitted from this embodiment. Although this embodiment provides advantages with regard to polarization diversity and minimization of polarization noise at the optical receiver, this embodiment has a small probability that an acceptable signal will not be present on one of fibers 136 and 138 .
- splitter 162 functions as described for splitter 62 . Fibers 164 , 168 and the input fiber to splitter 162 need not be PMF except if needed for splitter 162 to function as required.
- FIG. 4 illustrates a method in accordance with an embodiment of the present invention in which three optical fibers are utilized to transmit polarization diverse representations of a signal to an optical receiver. It will be understood that this method can also apply where only two optical fibers are utilized by eliminating reference to a third fiber/light beam.
- step 202 first, second and third light beams are generated at a site remote from the optic receiver where each carries a polarization diverse representation of the same information.
- the first, second and third light beams are transmitted on respective first, second and third fibers to an optical receiver.
- the polarization diverse signals are carried by separate fibers at least through the region experiencing vibration.
- the amplitudes of the received information on each fiber are compared for a concurrent time frame.
- the largest amplitude signal or best quality signal is selected and decoded at the optical receiver in order to recover the encoded information carried by the light beam.
- the fibers carrying the respective light beams can be single mode fibers.
- the sensor 42 is a Mach-Zehnder interferometer having a basic structure such as described in FIG. 1 of U.S. Pat. No. 5,448,058.
- the “return lead” of the interferometer which carries the useful signal information of the two interfering light beams, consists of fiber 44 .
- Two elliptically polarized fields representing light from the two legs of a fiber optic sensor, e.g. a Mach-Zehnder interferometer, are incident on beamsplitter 50 .
- A ( cos ⁇ ( ⁇ ) i * sin ⁇ ( ⁇ ) ) ⁇ ⁇
- B ( cos ⁇ ( ⁇ ) i * sin ⁇ ( ⁇ ) ) ( Eq . ⁇ 1 )
- Angles ⁇ and ⁇ range from ⁇ 45° to +45°. The tangent of the angle gives the ratio of the minor to major axis.
- Rotation angles are x for field A and y for field B.
- Reflection and transmission matrices of field amplitudes A and B at beamsplitter 50 are given by equations 5-1 and 5-2:
- R ⁇ ⁇ 1 ( R s ⁇ exp ⁇ ( i ⁇ ⁇ 0 ) 0 0 R f ⁇ exp ⁇ ( i ⁇ ⁇ 1 ) ) ( Eq . ⁇ 5 ⁇ - ⁇ 1 )
- T ⁇ ⁇ 1 ( T s ⁇ exp ⁇ ( i ⁇ ⁇ 2 ) 0 0 T f ⁇ exp ⁇ ( i ⁇ ⁇ 3 ) ) ( Eq .
- Arbitrary phase factors ⁇ 0 , ⁇ 1 , ⁇ 2 and ⁇ 3 represent propagation of the light down the fast and slow axes of the PM fibers after the beam splitting operations.
- the 45° rotation at the 45° PMF to PMF splice 58 is represented by a 45° rotation matrix (Rot 45 ) and the beam separation of beamsplitter 62 is given by two polarization matrices (P2 in the x axis and P3 in the y axis) in the 45° angle rotated coordinate system as:
- Transmission matrices of equation 7 represent the propagation of light from the input of beamsplitter 50 to the two outputs of beamsplitter 62 . They are products of the matrices in equations 5 and 6.
- T 2 P 2 *Rot 45 *T 1
- T 3 P 3 *Rot 45 *T 1 (Eq. 7)
- a 1( x ) R 1 *A ( x )
- a 2( x ) T 2 *A ( x )
- a 3( x ) T 3 *A ( x ) (Eq. 8-1)
- B 1( y ) R 1 *B ( y )
- B 2( y ) T 2 *B ( y )
- B 3( y ) T 3 *B ( y ) (Eq. 8-2)
- the useful beat signals presented to the optical receiver are products of fields A and B at fibers 34 , 38 and 36 , respectively.
- H 1( x,y )
- H 2( x,y )
- H 3( x,y )
- the bar above portions of factors in equation 9 represents the complex conjugate of the factor.
- the maximum beat signal among the three signals presented by fibers 34 , 38 and 36 is used for signal recovery by the polarization diversity receiver.
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Abstract
Description
- The invention relates generally to optical signal transmission and is particularly, but not exclusively, suited for systems where phase information is transmitted over an optical cable to a remotely located optical receiver where the optical cable is subject to vibration due to the external environment.
- Optical cable (fiber) is utilized in a variety of applications to carry information that is modulated onto a beam of light. In some applications significant portions of the optical cable are in an environment where the optical cable is not normally subjected to substantial physical vibration. In other applications optical cable is utilized to carry information between two locations where the optical cable is subject to substantial movement, flexing or vibration.
-
FIG. 1 illustrates an example of an application where theoptical cable 10 is subject to substantial movement. In this application phase information is transmitted from atowed array 12 of acoustic sensors towed behind awatercraft 14 to anoptical receiver 16 in the watercraft. An optical sensor 18 may use a Mach-Zehnder interferometer as described in U.S. Pat. No. 5,448,058 and incorporated herein by reference. One or more light beams carrying the sensed information are transmitted to the optical receiver by one or more optic fibers inoptical cable 10. A light source, e.g. a laser, is associated with thereceiver 16 and transmits a light beam on one fiber of thecable 10 as an input to the sensor which is typically a passive device such as an interferometer. Anothercable 20, e.g. a steel cable, absorbs the forces required to pull the sensor array through the water. In this environment the optical cable experiences substantial physical movement, i.e. low-frequency vibration typically below 50 hertz known as tow cable strum. - Movement of an optical cable carrying information encoded on a light beam can give rise to a change in the state of polarization of the transmitted light. Unwanted changes in the state of polarization of the transmitted light such as due to tow cable strum are manifest as polarization noise at the optical receiver.
- Polarization diversity detection has been utilized in an optical receiver to overcome polarization fading. The desired signal can disappear at the optical receiver due to polarization fading such as when the two light beams in a Mach-Zehnder interferometer are orthogonal. A polarization diversity receiver is described in U.S. Pat. No. 5,852,507, which is incorporated herein by reference. Polarization optics or masks have been employed at the receiver adjacent to the detector elements to achieve polarization diversity reception.
- However, rapidly changing states of polarization of the transmitted light, such as due to tow cable strum, can create sufficient polarization noise at the receiver to substantially impair the detection of the transmitted optical signal. Polarization masks or shifters used at the receiver prior to signal detection are useful in helping to eliminate signal fading due to polarization crossing but also induce unwanted polarization noise at the receiver when the light beam carrying the signal is subjected to undesired changes of polarization state. Thus, there exists a need for an improved optical system that can take advantage of polarization diversity while minimizing difficulties with polarization noise.
- It is an object of the invention to provide a solution that substantially satisfies this need.
- The invention in one implementation encompasses an apparatus. The apparatus includes at least one polarization beamsplitter that receives as an input a single light beam carrying sensor information and produces two light beams with polarization diversity. These two beams each carry sensor information contained in the single originating light beam. This apparatus is located at or near the point of origination of information that is to be conveyed to a remotely located optical receiver. Separate optic fibers carry each of the two beams to the remote location where the information is recovered by an optical receiver from the two separate light beams.
- In a further implementation, the apparatus includes means for producing three separate light beams from a single light beam where each of the three beams is polarization diverse from the other beams. Three separate optic fibers carry respectively each of the three beams from the point of origination to the remote location where the information is recovered by an optical receiver from the three separate light beams.
- Another implementation of the invention encompasses an exemplary method. The method includes generating, at or adjacent the point of origination of information to be conveyed to a remotely located optical receiver, at least two light beams that are polarization diverse to each other that each carries a representation of the same information. These two light beams may be converted into two single mode type light beams. Separate optic fibers transmit the single mode light beams to the remote location where an optical receiver selects one of the light beams for decoding the signal information.
- Features of exemplary implementations of the invention will become apparent from the description, the claims, and the accompanying drawings in which:
-
FIG. 1 shows a known system in which an optic cable is subject to a vibration inducing environment. -
FIG. 2 is a representation of one implementation of an apparatus in accordance with the present invention in which three light beams with polarization diversity are carried by respective optic fibers through a portion of the environment that subjects the fibers to vibration. -
FIG. 3 is a representation of another implementation of an apparatus in accordance with the present invention in which two light beams with polarization diversity are carried by respective optic fibers through a portion of the environment that subjects the fibers to vibration. -
FIG. 4 is an exemplary method in accordance with the present invention. - An aspect of the present invention resides in the recognition of the mechanism by which polarization noise occurs and in appreciating an energy transfer characteristic of a light beam carried by an optical fiber as a function of polarization changes. Although polarization diversity detection has been employed within known optic receivers, polarization noise caused by vibration of the optic fiber has provided an adverse impact in being able to accurately decode the transmitted signal. In considering this problem, an inventive contribution was made when the total transmitted power of the light beam was considered from a different perspective. In traveling from the sensor output to the detector at the optical receiver, the time-dependent characteristic of the total transmitted power of the light beam should remain the same except for the overall attenuation loss. This principle applies even in the presence of undesired polarization changes due to cable vibration. Thus, a single light detector, e.g. a photodiode, at the optical receiver which collects all of the light from a single cable should reflect the time-dependent power characteristic of the light beam with or without undesired polarization changes. Therefore, generating polarization diverse signals at or adjacent the signal source and transmitting the polarization diverse light beams on separate optic fibers, even if these fibers are subjected to vibrations causing undesired polarization changes, can be decoded by separate detectors at the optical receiver with minimized interference due to polarization noise.
-
FIG. 2 illustrates an embodiment of the present invention in which asensor system 30 transmits information by light beams carried by corresponding optical fibers tooptical receiver 32. This embodiment is especially, but not exclusively, suited for the transmission of information returned by acoustic sensors, e.g. interferometers, on a towed sensor array where thesystem 30 is on the towed sensor array andoptical receiver 32 is on a watercraft that tows the array. Theoptical fibers 34, 36 and 38 carry polarization diverse light beams transmitted fromsystem 30 to corresponding detectors in theoptical receiver 32. These optical fibers experience substantial physical vibration, e.g. towed cable strum, inregion 40 of the optical fibers extending between the watercraft carryingoptical receiver 32 and thesignal origination system 30 on the towed sensor array. Alight source 33, a laser, transmits a light beam carried byfiber 35 that serves as the input tosensors 42. The fibers passing throughregion 40 may be part of one cable. - The
sensor 42 which may comprise an acoustic sensor, e.g. a Mach-Zehnder interferometer, provides an output signal as a light beam carried by asingle mode fiber 44. Asplice 46 converts the light beam from a single mode fiber type (SMF) to a polarization maintained fiber type (PMF). The output light beam fromsplice 46 is carried byPMF 48 to a polarization maintainingbeam splitter 50, which may comprise a fiber optic implementation available from Canadian Instrumentation and Research, that splits the incoming beam into two beams. One output beam fromsplitter 50 is carried by PMF 52 tosplice 54 that converts the light beam from PMF type to SMF type. The other output beam fromsplitter 50 is passed byPMF 56 to a 45° PMF toPMF splice 58, which provides a 45° rotation of the polarization eignmstates. This beam is carried byPMF 60 to polarization maintainingbeam splitter 62, which may comprise a fiber optic implementation available from Canadian Instrumentation and Research that splits the incoming beam into two PMF beams. One output beam fromsplitter 62 is carried byPMF 64 to the PMF toSMF splice 66. The other output beam fromsplitter 62 is carried by PMF 68 to PMF toSMF splice 70.Splices separate SMFs 34, 36 and 38, respectively. Although a conversion is shown from PMF to SMF at these three splices, PMF fiber could be used to carry the light beams to the optical receiver. These three SMFs each carry a representation of the same instance (same time frame) of an output signal fromsensor 42 and traverseregion 40 which subjects the fibers to vibration. The light beams carried by these three fibers are terminated respectively atoptical receiver 32 containing three separate photodiode detectors coupled respectively to each SMF. - For this embodiment, the
PM fibers PMF splice 58 are needed betweensplitter fibers splitters - The following values and parameters can be utilized in the exemplary embodiment as shown in
FIG. 2 . With respect tobeam splitter 50, for light along the slow axis of thePMF 48, 67% is coupled toPMF PMF 56. For light along the fast axis ofPMF 48, 100% is transmitted toPMF 56. With respect to the light beam onPMF 60, 100% of the fast axis light is coupled bybeam splitter 62 toPMF 68, and 100% of the slow axis light is coupled toPMF 64. As an alternative to using a separate 45° PMF toPMF splice 58 andsplitter 62 with characteristics as described, a single device combining both functions, such as available from JDS Uniphase Corporation, could be used. -
FIG. 3 represents a further embodiment in whichsensor system 130 transmits information by light beams carried by correspondingoptical fibers optical receiver 132. Since this embodiment has substantial similarities to the embodiment explained with regard toFIG. 2 , only differences will be addressed. It will be understood that elements inFIG. 3 that correspond with like elements inFIG. 2 are numbered by adding “100” to the reference numeral of the corresponding element inFIG. 2 . Basically, the 45° PMF toPMF splice 58 of the embodiment ofFIG. 2 is omitted from this embodiment. Although this embodiment provides advantages with regard to polarization diversity and minimization of polarization noise at the optical receiver, this embodiment has a small probability that an acceptable signal will not be present on one offibers fibers FIG. 2 . The embodiment ofFIG. 2 has 100% probability that at least one of the three of the output light beams received by the optical receiver will not be orthogonal or crossed, e.g. at least one of the three will have an acceptable signal.Splitter 162 functions as described forsplitter 62.Fibers splitter 162 need not be PMF except if needed forsplitter 162 to function as required. -
FIG. 4 illustrates a method in accordance with an embodiment of the present invention in which three optical fibers are utilized to transmit polarization diverse representations of a signal to an optical receiver. It will be understood that this method can also apply where only two optical fibers are utilized by eliminating reference to a third fiber/light beam. Instep 202 first, second and third light beams are generated at a site remote from the optic receiver where each carries a polarization diverse representation of the same information. Instep 204 the first, second and third light beams are transmitted on respective first, second and third fibers to an optical receiver. In order to minimize the signal detection problems encountered due to the presence of polarization noise such as caused by physical vibration of an optical fiber carrying a light beam, the polarization diverse signals are carried by separate fibers at least through the region experiencing vibration. Instep 206 the amplitudes of the received information on each fiber are compared for a concurrent time frame. Instep 208 the largest amplitude signal or best quality signal is selected and decoded at the optical receiver in order to recover the encoded information carried by the light beam. The fibers carrying the respective light beams can be single mode fibers. - A detailed analysis of the signals generated by
origination system 30 follows and concludes with equations that describe the useful beat signals presented to the optical receiver for each fiber. This example assumes that thesensor 42 is a Mach-Zehnder interferometer having a basic structure such as described in FIG. 1 of U.S. Pat. No. 5,448,058. As shown inFIG. 2 of the present embodiment, the “return lead” of the interferometer, which carries the useful signal information of the two interfering light beams, consists offiber 44. - Two elliptically polarized fields representing light from the two legs of a fiber optic sensor, e.g. a Mach-Zehnder interferometer, are incident on
beamsplitter 50. In their principal axis coordinate systems, they are:
Angles α and β range from −45° to +45°. The tangent of the angle gives the ratio of the minor to major axis. The absolute values of α and β are 45° for right and left circularly polarized light and zero for linearly polarized light.
The following rotation matrices are used to express the fields in a common coordinate system along the fast and slow axes of the PM fiber.
Rotation angles are x for field A and y for field B. They range from zero to 180°. The fields in the new coordinate system are:
A(x)=Rot(x)·A B(y)=Rot(y)·B (Eq. 3)
Atbeamsplitter 50, the power reflection and transmission coefficients for fast and slow axes are:
Rf=0 Tf=1.00 Rs=0.667 Ts=0.333 (Eq. 4)
Reflection and transmission matrices of field amplitudes A and B atbeamsplitter 50 are given by equations 5-1 and 5-2:
Arbitrary phase factors θ0, θ1, θ2 and θ3 represent propagation of the light down the fast and slow axes of the PM fibers after the beam splitting operations.
Afterbeamsplitter 50, the 45° rotation at the 45° PMF toPMF splice 58 is represented by a 45° rotation matrix (Rot45) and the beam separation ofbeamsplitter 62 is given by two polarization matrices (P2 in the x axis and P3 in the y axis) in the 45° angle rotated coordinate system as:
Transmission matrices of equation 7 represent the propagation of light from the input ofbeamsplitter 50 to the two outputs ofbeamsplitter 62. They are products of the matrices in equations 5 and 6.
T2=P2*Rot 45 *T1 T3=P3*Rot 45 *T1 (Eq. 7)
Propagation matrices R1, T2 and T3 characterized light propagation from the input ofbeamsplitter 50 to theoutput fibers 34, 38 and 36, respectively. The transformed fields A and B atfibers 34, 38 and 36 are given by equations 8-1 and 8-2:
A1(x)=R1*A(x) A2(x)=T2*A(x) A3(x)=T3*A(x) (Eq. 8-1)
B1(y)=R1*B(y) B2(y)=T2*B(y) B3(y)=T3*B(y) (Eq. 8-2)
The useful beat signals presented to the optical receiver are products of fields A and B atfibers 34, 38 and 36, respectively. The respective magnitudes are:
H1(x,y)=|A1(x)*{overscore (B1(y))}| H2(x,y)=|A2(x)*{overscore (B2(y))}| H3(x,y)=|A3(x)*{overscore (B3(y))}| (Eq. 9)
The bar above portions of factors in equation 9 represents the complex conjugate of the factor. In practice, the maximum beat signal among the three signals presented byfibers 34, 38 and 36 is used for signal recovery by the polarization diversity receiver. - Using the above equations, an empirical study was made to identify the worst case (minimum magnitude) for the maximum available signal. Rotation angles of x and y from zero to 180° for the input fields of A and B were considered. Elliptical polarization angles α and β as well as arbitrary phase factors θ0, θ1, θ2 and θ3 were utilized as adjustable parameters. By varying angles α, β, x and y in a systematic way as well as by varying phase factors θ0, θ1, θ2 and θ3 the lowest possible maximum beat signal was obtained. The results of the study found a minimum of the maximum beat signal of 0.25 and a maximum beat signal of 0.667. These values are based on a reference of 1.0 representing the maximum beat signal obtained by a single photodiode at the optical receiver without any polarization masks.
- For the embodiment of the present invention as shown in
FIG. 3 that utilizes two instead of three optic fibers carrying polarization diverse signals, this system still offers advantages in overcoming polarization noise but has a small chance that a usable signal will not be present on either fiber. For the worst case of the minimum value of the maximum beat signal presented byfibers optical receiver 132, the signal can go to zero. It was determined that a probability of 0.8% exists that an output beat signal presented byfiber FIG. 2 . The embodiment described inFIG. 3 does provide an improvement in minimizing polarization noise due to tow cable strum. Problems arising from polarization noise due to vibrations of all types, i.e. periodic, aperiodic and random vibrations, are all minimized by the techniques of the present invention. - Various modifications and additions can be made to the illustrative embodiments. For example, more than three light beams carried by more than three optic fibers could be used. Although polarization noise is minimized by using polarization diverse signals carried by separate fibers in the illustrative embodiments between the entirely of the path from origination to optical receiver, only using this technique in the region of vibration is required. Thus, it is not necessary that separate fibers with separate polarization diverse light beams be used for the whole path. For example, the polarization diverse signals could be generated just prior to entry into the region of vibration, as opposed to being generated at or adjacent the origination signal source. Various types of optic and fiber devices can be used to produce polarization diverse light beams.
- The steps or operations described herein are just exemplary. There may be many variations to these steps or operations without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified.
- Although exemplary implementations of the invention have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.
Claims (23)
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EP06719814.3A EP1851519B1 (en) | 2005-02-22 | 2006-01-30 | Polarization diversity for optical fiber applications |
PCT/US2006/003125 WO2006091334A1 (en) | 2005-02-22 | 2006-01-30 | Polarization diversity for optical fiber applications |
CA2598274A CA2598274C (en) | 2005-02-22 | 2006-01-30 | Polarization diversity for optical fiber applications |
US12/454,115 US7876644B2 (en) | 2005-02-22 | 2009-05-13 | Polarizaton diversity for optical fiber applications |
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CN111785004A (en) * | 2020-07-01 | 2020-10-16 | 上海广拓信息技术有限公司 | Line patrol information transmission method and system |
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US20120237205A1 (en) * | 2011-03-16 | 2012-09-20 | Baker Hughes Incorporated | System and method to compensate for arbitrary optical fiber lead-ins in an optical frequency domain reflectometry system |
US9546915B2 (en) | 2011-10-12 | 2017-01-17 | Baker Hughes Incorporated | Enhancing functionality of reflectometry based systems using parallel mixing operations |
US9009003B1 (en) | 2012-05-03 | 2015-04-14 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Apparatus and method for elimination of polarization-induced fading in fiber-optic sensor system |
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US5127066A (en) * | 1989-11-14 | 1992-06-30 | Cselt - Centro Studi E Laboratori Telecommunicazioni S.P.A. | Coherent optical-fiber communication system using polarization diversity transmission |
US5140453A (en) * | 1987-03-13 | 1992-08-18 | Hitachi, Ltd. | Optical receiving method utilizing polarization diversity and apparatus for carrying out the same |
US5798834A (en) * | 1996-04-10 | 1998-08-25 | Loral Defense Systems | Interferometric fiber optic method and apparatus for obtaining absolute static measurement using an optical frequency-time profile |
US6490045B1 (en) * | 1998-10-09 | 2002-12-03 | University Of Southhampton | Fibre optic sensor |
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DE3481449D1 (en) * | 1984-09-18 | 1990-04-05 | Western Atlas Int Inc | SEA ICE MIXED PROBE. |
GB2199713A (en) | 1986-12-31 | 1988-07-13 | Stc Plc | Optical communication system |
NO322073B1 (en) | 1999-06-23 | 2006-08-07 | Optoplan As | Polarization Control Procedure |
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2005
- 2005-02-22 US US11/062,649 patent/US7554885B2/en active Active
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US5140453A (en) * | 1987-03-13 | 1992-08-18 | Hitachi, Ltd. | Optical receiving method utilizing polarization diversity and apparatus for carrying out the same |
US5127066A (en) * | 1989-11-14 | 1992-06-30 | Cselt - Centro Studi E Laboratori Telecommunicazioni S.P.A. | Coherent optical-fiber communication system using polarization diversity transmission |
US5798834A (en) * | 1996-04-10 | 1998-08-25 | Loral Defense Systems | Interferometric fiber optic method and apparatus for obtaining absolute static measurement using an optical frequency-time profile |
US6490045B1 (en) * | 1998-10-09 | 2002-12-03 | University Of Southhampton | Fibre optic sensor |
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CN111785004A (en) * | 2020-07-01 | 2020-10-16 | 上海广拓信息技术有限公司 | Line patrol information transmission method and system |
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US7876644B2 (en) | 2011-01-25 |
US7554885B2 (en) | 2009-06-30 |
US20090263136A1 (en) | 2009-10-22 |
EP1851519A1 (en) | 2007-11-07 |
WO2006091334A1 (en) | 2006-08-31 |
CA2598274C (en) | 2014-10-21 |
CA2598274A1 (en) | 2006-08-31 |
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